1. Field of the Invention
The present invention relates to an impact transmitting device which is used in impact monitoring operations. More particularly, the present invention relates to an apparatus for detecting and reporting mechanical impact events in reciprocating machines.
2. Description of the Prior Art
The principle of operation of an impact transmitting device for reciprocating machines is to detect free vibrations which are typically symptomatic of machine failure and to transmit the free vibration measurements in the form of an electrical signal. This electrical signal is received by an external logic solver which determines whether or not the reciprocating machine should be powered down. In practice, an impact transmitting device saves unnecessary waste caused by speculative preventative maintenance and increases the life-cycle of reciprocating machine components by alerting operators to early-stage development of harmful mechanical conditions. Such conditions may include loose rod nuts, loose bolts, excessive slipper clearance, worn pins, broken parts, liquid in the process, and rubbing.
In operation, an impact transmitting device is mounted to a reciprocating machine such as a reciprocating compressor having a compressor cylinder assembly. The impact transmitting device detects mechanical impact events in or near the compressor cylinder assembly. The amplitude of each detected impact event is compared to a preset threshold level. If the amplitude of the impact event surpasses the threshold, then the impact event is counted as an xe2x80x9cabove-threshold impact event.xe2x80x9d The number of above-threshold impact events that are counted by the impact transmitting device during a preset time window interval is reported to an external logic solver such as a programmable logic controller (xe2x80x9cPLCxe2x80x9d) or distributed control system (xe2x80x9cDCSxe2x80x9d). The external logic solver compares the signal to a predetermined level of acceptable above-threshold impact events during the given time window. If the number of above-threshold level impact events is below the preset acceptable level, then the impact events are disregarded as a xe2x80x9cnuisance alarm.xe2x80x9d However, if the number is at or above the acceptable level, then the machine is experiencing harmful mechanical events and must be shut down for appropriate maintenance.
While prior art impact transmitting devices offer the ability to detect and report useful mechanical impact data, it has been observed that these devices have at least two deficiencies. First, prior art impact transmitting devices are actually stand-alone rack mounted monitoring systems. As a result, prior art impact transmitting devices are expensive and cumbersome. Second, many prior art impact transmitting devices do not provide for manipulation of the impact threshold level or the time window interval during which the above-threshold impact events are counted. Moreover, the impact transmitter devices that do allow these parameters to be manipulated must be adjusted by using software prior to installation of the device or by an experienced technical person.
Accordingly, it would be desirable to have an impact transmitting device that functions as a single self-contained unit. Moreover, it would be desirable to have an impact transmitting device having a simple xe2x80x9cfieldxe2x80x9d adjustable impact threshold level for detecting above-threshold level impact events and a simple xe2x80x9cfieldxe2x80x9d adjustable time window interval during which these above-threshold level impact events are counted. These novel and useful results have been achieved by the present invention.
In accordance with the present invention, apparatus is provided for impact measurement and transmission for reciprocating machines.
An impact transmitting device in accordance with the present invention provides for the detection and transmission of (1) the quantity of severe impacts during a time window interval, and (2) the severity of the impacts above a static threshold. This impact quantity and severity measurement is used to differentiate singular xe2x80x9cnuisance alarmxe2x80x9d impacts from repeat xe2x80x9cmachine failurexe2x80x9d impacts.
An impact transmitting device in accordance with the present invention further provides a single self-contained unit comprising a stainless steel housing which contains an impact accelerometer, a detector circuit, a measurement and timing circuit, a 4-20 mA driver circuit, independent polarity circuit, and an electromagnetic impulse protection unit.
An impact transmitting device in accordance with the present invention still further provides a field adjustable static threshold defining the severity of the impact, and a field adjustable reference time window interval. The variable severe impact level threshold allows an operator to isolate severe impacts from typical machine vibration. The variable time window interval allows an operator to synchronize the present invention with different machine speeds and to collect severe impact data over an appropriate time frame.
An impact transmitting device in accordance with the present invention also provides functionality independent of the polarity of the power of a PLC or DCS.